The primary objective of the studies outlined in this proposal is to elucidate more fully the overall role of the kidney in systemic acid-base homeostais. During previous years studies have been designed to investigate the basic mechanism(s) responsible for urinary acidification and the regulation of this process in several nephorn segments, the maintenance of elevated CO2 tensions in the renal cortex, and the utility of urinary COs tension as a qualitative index of H+ secretion by the terminal nephron. The present application proposes to continue our investigation of fundamental mechanisms of the acidification process, but places major emphasis on investigation of the mechanism of impaired urinary acidification in experimental models of deranged acid- base and/or electrolyte balance. In order to accomplish these goals four specific projects are proposed: 1) Evaluation of acidification parameters in experimental models of distal renal tubular acidosis and selective aldosterone deficiency. 2) Evaluation of segmental ammonia transport in medullary and cortical nephrons to determine the role of ammonia transfer from the loop of Henle to the collecting duct in urinary ammonium excretion during changes in systemic potassium balance, mineralocorticoid deficiency and ureteral obstruction. 3) Evaluation of the role of transepithelial pH gradients in the regulation of H+ secretion by the proximal convoluted tubule. 4) Evaluation of the mechanism and kinetics of H+ secretion in human brush border membrane vesicles in vitro and to compare these findings with other mammaliam species. An important advantage of the in vivo micropuncture studies proposed in this application is the capability in our laboratory of extending these observations by investigation similar questions in the isolated perfused tubule in vitro. The maintenance of acid-base balance is an essential physiological role of the kidney. The control of this process must be understood to fully elucidate these functions. The study of models of deranged acidification, such as renal tubular acidosis, may enhance our understanding of this disease in humans, and improve our ability to diagnose this condition early in the course of the disease.